Diving in marine sports is very popular among young people, and various electronic wristwatches having depth measuring functions, i.e., so-called diver's watches have been developed accordingly.
An electronic wristwatch with a depth measuring function of this type is exemplified by the following electronic wristwatch (e.g., Japanese Utility Model Laid-Open Nos. 60-183895 and 60-183896). In this wristwatch, to minimize the power consumption by operating a depth measuring circuit during only actual diving because the depth measuring circuit has a very high current consumption, a power switch and a main switch such as a mode selection switch are arranged independently of a water detecting means. When the main switch is set in an ON state and the water detecting means is set in an ON state upon detecting that the wristwatch has become wet with water or salt water. A transparent electrode formed on the surface of the cover glass of the electronic wristwatch is used as the water detecting means. The water detecting means detects a change in conduction resistance or capacitance when water or salt water comes in contact with this electrode.
An automatic sounding thermometer described in Japanese Patent Laid-Open No. 55-80010 comprises an underwater operation switch serving as a water detecting means for detecting a water pressure or the electrical resistance of salt water, a power switch, and a start switch. When the start switch is turned on upon a turn-0N operation of the power switch, the underwater operation switch is started by the water pressure or salt water, thereby driving the depth measuring circuit.
Generally, a beginner becomes nervous before diving, and his/her mind is too much occupied with diving. For this reason, even if the diver has the above-described electronic wristwatch with the depth measuring function, he/she often forgets to turn on the main switch before diving. As a result, depth measurement cannot be performed at all, or it is too late to turn on the switch during diving.
To prevent the failure of depth measurement due to forgetting of a turn-ON operation of the switch, a specialized depth measurement device was proposed in Japanese Patent Laid-Open No. 59-18415 in which only a water detecting means for detecting if the wristwatch is wet with water is arranged while omitting a main switch. When this water detecting means detects water, depth measurement is started. However, this prior art disclosed in Japanese Patent Laid-Open No. 59-18415 is not a device incorporated in an electronic wristwatch but a specialized depth measurement device having a simple structure. All circuits are normally set in an inoperative state. All the circuits including a display driving circuit are set in an operative state in accordance with a signal from the water detecting means, thereby performing depth measurement.
Since a diver wears such a specialized depth measurement device on a wrist immediately before diving, no problem is posed. However, as for a wristwatch with such a depth measuring function, the wristwatch is worn on the wrist also during non-diving, so it may get wet with rain or at the time of face washing. In this case, the water detecting means detects water to start a depth measuring operation, and at the same time, display is switched from time display to depth display. This causes instantaneous confusion, or an operation for returning the display to the original time display need to be performed.
On the other hand, in a general electronic equipment with a depth measuring function, the main switch is operated to measure and store a 0-m depth reference pressure before diving depth measurement. After diving is started, a diving depth is calculated from a relative pressure value with respect to the 0-m reference pressure value by the water detecting means.
The device disclosed in Japanese Patent Laid-Open No. 59-18415 comprises no main switch. For this reason, the first output value (pressure value) obtained when the water detecting means detects that the device comes underwater is used as a 0-m depth reference pressure value.
However, the depth at the start of diving may instantaneously reach 1 m or more, and in some cases, several m although it differs depending on diving styles. Therefore, in the above method of measuring the reference value, a pressure value to be actually measured corresponds to a reference value not at a depth of 0 m but at a depth of 1 to several m. For this reason, in subsequent depth calculation using this pressure value as a 0-m depth reference pressure value, a depth error corresponding to 1 to several m is generated.
In addition, in the electronic equipment with the depth measuring function of this type, after a current starts to flow through a pressure sensor in accordance with a signal from the water detecting means, a predetermined period of time is required until the circuit is stabilized, and A/D conversion and calculation of the depth value is completed. When this delay of time is taken into consideration, the depth measurement error caused due to the above 0-m depth reference pressure error increases further.
All of the electronic equipments with the depth measuring function disclosed in Japanese Utility Model Laid-Open Nos. 60-183895 and 60-183896, the automatic sounding thermometer disclosed in Japanese Patent Laid-Open No. 55-80010, and the device having only the water detecting means in Japanese Patent Laid-Open No. 59-18415 have the following problem after diving. That is, if water or salt water remains on the water detecting means, or salt, dust, or dirt adheres to the water detecting means after diving, the water detecting means determines that the device is underwater on the basis of a change in conduction resistance or capacitance, and the depth measuring circuit continues to operate. As a result, an unexpected increase in current consumption causes run down of a battery.
The present invention has been made in consideration of the above situations, and has as its first object to provide an electronic equipment with a depth measuring function in which a program for display switching from normal display such as a time to depth measurement display by a water detecting means is provided, thereby improving convenience.
The present invention has as its second object to provide an electronic equipment with a depth measuring function, which performs measurement of the 0-m depth reference pressure as accurately as possible, thereby minimizing a depth measurement error.
The present invention has as its third object to provide an electronic equipment with a depth measuring function, which minimizes the battery consumption after diving.